Distillation of oxo alcohols



March 11, 1952 Filed Dec. 31 1948 C. E. MORRELL ET AL DISTILLATION OF' OXO ALCOHOLS 2 SHEETS-SHEET l sa* 7W [1M March 11, 1952 c. E. MORRELI. ET AL 2,589,018

ADISTILLATI01\1 0F oxo ALCoHoLs Filed Dec. 31, 1948 2 SHEETS-SHEET 2 Condenser 33g, @76M @HKM/W Patented Mar. ll, 1952 UNITED STATES PATENT OFFICE DISTILLA'TION 0F 0X0 ALCOHOLS Charles=E..Morrell, =Westfeld, Frank A. Biribauer, Cranford, `and. Carl S. Carlson, Roselle, N. J., assignors to Standard Oil Development Comr pany, a corporation of Delaware ApplicationDecember 3l, 1948,` Serial No. 68,472

(i-Claims. 1

This invention relates to van improved `process for the purication of `crude alcohols, by a distillation method, and more specifically, .to `a `method for purifying higher boiling alcohols which contain impurities of the type tending `to undergo decomposition at .the normal `boiling point of the alcohol or alcohols in question.

Manyalcohols which are of great commercial importance are prepared by synthetic processes and especially b y the so-called oxo reaction. The term oxo reaction is a general term used .to describe the preparation of oxygenated organic compounds by the reaction of carbon monoxide and hydrogen with olefinic hydrocarbons in the presence of a carbonylation catalyst. Themethod is used particularly vfor the manufacture `of various primary alcohols, specifically octyl alcohols, by operationsinvolving Ainteraction of carbon monoxide, hydrogen, a `hydrocarbon mixture containingsubstantial amounts of heptenes, and a cobalt carbonylation catalyst to form octyl `aldehydes, and Vsubsequent reduction or these `aldehydesby catalytic hydrogenation to a mixture Arelatively high in octyl alcohols.

Primaryalcohols of this general type are .of great economic 'importance and interest because ci' theiruse asintermediatesin the manufacture of `plasticizers of'thedieester type. These alcohols have previously been supplied vmainly by such comparatively Acostly procedures as aldcl condensation of butyraldehydea followed by deu hydration, and hydrogenation ofthe resulting unsaturated octyl aldehyde. The oxo reaction and subsequent 'hydrogenation `have been found to Acomprise a highly economical and valuable method for manufacturing octyl valcohols from `cheap and readily available hydrocarbon material.

vIn the oxo or carbonylation stage ofthe proc- `ess a large number of different types `of `reaction take placeto form a `variety of products. One of the primary reaction products will bealdehydes. These aldehydes 'themselves can undergo further reactions Ato yield other products. `For instance, thealdehydes condense With each other to yield aldols. At least a part `of the aldols undergo dehydration `to alpha-beta-unsaturated aldehydes. Some ketones are'also formed under the reaction conditions. A part ofthe aldehydes formed in the reaction zone are hydrogenated to alcohols and the alcohols so formed react with aldehydes and ketones presentito give mixtures of acetal'sghemi-acetals, `and ketals. These compounds can undergo `further reactions, including dehydration, to ,give-ethers,fparticularly those of the unsaturated'types. The alcohols can esterify the acids present to give esters. .Hydrogenation `of a part of the olen starting feed stock, ,as

`Well as some deoxygenation of oxygenated intermediates, gives some hydrocarbons in Vthe final oxo product. In addition, other more complex and less known reactions also occur betweenthe various intermediates and products obtained `thereby yielding a mixture of higher boiling imcols, acetals, `lretals and esters are hydrogenated .in the presence of a suitable catalyst to `yield more saturated products containing ahigherpercentage of alcohols and non-olenic compounds. Some of these impurities, especially the `unsaturated ethers, acetals, ketals, aldols and esters are quite unstable towardheat andthe hydrolytic action of Water. For instance, in general, the aldols, acetals, hemiacetals and ketals have a great tendency to undergo degradative decomposition reactions Whenever the alcohol is. subjected to a simple distillation regardless of `Whether the distillation be carried out at superatrnospheric, atmospheric, or subatmospheric pressures. vIn many cases, thermally unstable esters are present and undergo both thermal and hydrolytic'decompositions under distillation conditions.

To be'more speciiic, if a crude Afraction ofiso'- octyl alcohol as produced by the oxonation Iof C'lolens, followed by hydrogenation, -isidistilled either in a batch or continuous manner andcuts removed according to increasing boiling point, then it is quite possible to obtain the following fractions:

l. A fraction `containing unconverted .oleiin hydrocarbons, saturated hydrocarbons, :and unhydrogenated aldehydes.

-2. A fraction containing principally isooctyl alcohol contaminated With decomposition products of aldols, herni-acetalaacetals, ketals,.:esters,

ethers, and the like.

:3. A fraction containing higher boiling materials includingesters and unsaturatesof low volyatility, higher alcohols, decomposition products an appreciable extent at the distillation temperature of the alcohol being "purified, in this particular ca se, the isooctyl alcohol. The decomposition reactions occurring always produce Water, especially by aldol dehydration, and this water probably contributes further to decomposition reactions by its hydrolytic action, especially on esters, ketalS, acetals and unsaturated ethers. The more volatile of the decomposition products, including Various saturated and unsaturated aldehydes, water, and alcohols (including both isooctyl and other alcohols of lower boiling point), go overhead with the alcohol product and contaminate the latter. Any aldehydes which are, in general, quite volatile, are distilled over with the alcohol fraction in this manner and can subsequently combine very readily with the distilled alcohol product, reforming acetals and hemiacetals, which are likewise subject to a second decomposition process when a redistillation of the alcohol fraction is attempted. Furthermore, aldehyde and other decomposition products are objectionable because they lower over-all product purity, and, due to instability, cause diiculties in the use of the alcohol. It is believed, however,

' that this is an oversimplied and incomplete picture of the over-all situation.

It can readily be seen that it is .difcult, if not impossible, to remove completely these acetals,

valdehydes, and other interfering impurities from alcohols produced by such methods as the oxo reaction using straight distillation using successive steps for removing fractions of increasing boiling points. The presence of free aldehydes or potentially free aldehydes such as acetals or hemi-acetals in any kind of commercial alcohol product is objectionable for a number of reasons. First of all, the aldehydic compounds are relatively unstable toward air, elevated temperatures, and other various regularly encountered conditions to which chemicals are exposed when stored. As a result, impurities such as color bodies are produced upon storage, especially under varying temperature conditions. Any aldehydes present also react readily with a part of the alcohol,

thereby reducing the amount of total alcohol present and the amount which would be readily available for other chemical reactions. Perhaps the most important commercial use for these higher molecular weight alcohols, such as the C8 isooctyl alcohols produced by the oxo reaction, is in esteriiication reactions to form compounds of the diester type for use as plasticizers in resin and plastic compositions. Those of the phthalate and adipate type are widely manufactured. Even though an alcohol product of a synthetic source -appears to be perfectly colorless, it frequently contains small amounts of impurities which form colored bodies during the subsequent acid--alcohol reaction. These colored materials are difficult to remove from the resulting high-boiling ester products and result in inferior esters which require additional and excessive purification prior to their use as plasticizers.

This same type of problem of unstable impurities also exists in connection with other alcohols made by the oxo reaction, particularly for the higher boiling `alcohols of the range of Cs to C15 Yor higher. For example, the C9 alcohols, prepared by the reaction of C8 oleiins such as diisobutylene with carbon monoxide and hydrogen may loev puried in the same manner as that described herein' for VVthe purication ofthe Ca oxo alcohols.

It Vcanthus be seen that it is of great desirability to obtain the alcohol products, particularly rthose of the type obtainable from synthetic proc- 'esses as the oxo process, as free of aldehydes,`

acetals and other chemically reactive and ii-1 stable substances as possible.

A very superior method has been found for accomplishing this purpose of getting pure alcohols relatively free from aldehydes and related impurities. This new method can be called a distillation type puriiication and consists essentially of at least two stages in a closely related sequence of operation.

This process can be used for purication of alcohols containing thermally unstable high boiling impurities obtained from any source, and is especially applicable to treatment of alcohols having from 4 to 15 carbon atoms. It nds particular application in purification of alcohols obtained by the so-called oxo reaction mentioned above and especially to alcohols of the Cs and C9 class, although the process can also be applied advantageously for other alcohols containing similar types of thermally unstable impurities, particularly alcohols obtained by hydrogenation of carbonyl compounds.

A typical Cs crude oxo alcohol mixture such as can be employed as starting feed in this improved purication process has the following composition:

Wt. percent Alcohol as CsY 65.0 Aldehyde as C8 1.8 Acetal as C24 3.7 Ester as C9 3.0 Unsaturates as C7 6.3 Acid as Ca 0.1 Water 2.0 Saturates and unknowns 18.1

In the first stage, there is carried out a Vaporization of the crude alcohol mixture including any acetals, hem-acetals, and other thermally and hydrolytically unstable compounds. This vaporization may be done in any type of conventional still column. One critical factor in this first stage vaporization or distillation is that the bottoms temperature must be maintained suiiiciently high to cause a substantial decomposition of the heat-unstable impurities, Vthereby releasing atleast a portion, and preferably a major portion, of the combined alcohol. This bottoms should always be above the normal boiling point of the alcohol, and generally considerably above it. The amount of material taken overhead comparative to the amount of bottoms allowed to remain in the still will depend on the degree of decomposition of acetals and other unstable compounds obtainable at the Vbottoms temperatureV employed as well on the precise composition of the impurities in the alcohol since some types of impurities may be'extremely resistant to thermal attack. 'y The overhead vapor temperature of the first distillation stage should not be greatly in excess of the normal boilingY range of the particular alcohol product which is being puried. In the case of isooctyl alcohol, the overhead temperature will be -185 C. Obviously, the bottoms Will be somewhat higher and may be considerably in excess of this, forV instance, for the isooctyl alcohols the bottoms temhead from the irst stage is passed "as Vquickly as possible, with yor without intermediate condensation, Ato a second `vaporization'or distillationcolumn. -A partial condenser may be used to return a part of the overhead Vto vthe lirst columnas reflux and ypass a part tothe second column. Here, all the materials presents in -the feed to the second column, and boiling at temperatures below the desiredalcohol product are `removed overhead from this column. Thisoverhead product will include any .decomposition `products boiling below the alcohol. `Itmust be emphasized .that a minimumof time and operation steps is of critical importance between the collecting of overhead vapor from the first stage distillation and `subjecting -these vapors to the ably as a vapor stream, Vfrom a point in the second column ata point located somewhat .below thepoint of Afeed of the overhead from the iirst column. By this procedure, it is possible to obtain a good alcohol product `relatively dry and iree of unwanted contaminants. The side stream -alcoholproduct may be taken toa third zone, if desired, for a further distillation or topping step.

A second procedure whichmay be followed for obtaining the product is carrying the total bottoms of the second distillation Zone, which contain the desired alcohol, to a third vaporization zone from which the puried product can be removed cverheadand thereby separated from the small quantityiof residual higher boiling materials.'

Other modications will also be suggested to one skilled in distillation techniques. In any case, regardless of the exact `manner in which the alcohol product is removed from the small quantity of residual high boilers, it is highly desii-able to maintain as low a bottoms temperature in the second vaporization step as possible and preferably not to allow a temperature appreciably higher than the boiling range of the alcohol itself. This precaution is, of course,` not a required one for the first distillation stage. In fact, it is highly desirable to maintain considerably higher temperatures in the first zone in order to decompose a greater amount of the high boiling impurities. One very convenient way `in which to maintain a low bottoms temperature in the second zone is to allow a certain amount of the alcohol to remain in the still bottoms in the second column.

lf very extensive thermal decomposition of the acetals and other high boiling materials has been obtained in the first stage, then it may be entirely possible to use somewhat higher temperatures in the alcohol recovery step.

Since, in general, for eflicient operation, it would seem desirable to recover ultimately the alcohol remaining in the bottoms from the alcohol recoverytowerfthese bottoms may be recycled to the rst distillation stages for further .decomposition.

Vtionating tower 2 The `degree of -purication .accomplished by this process can readily beevaluatedin any number of ways. Oneof thersimplest iis'byobservation of the number of degrees of spreadinlboiling range of the alcohol product obtained. As `is the general rule in chemical practice, the narrower boiling range is an indication that a purer product has been obtained. Color stability tests, `particularly those involving esterication, can also -be used to give an .indication yof .any color producing impurities present.

rIf so desired, `pressures other than atmospheric can be employed in either of ythese-stages. Under certain circumstances, the use of sub-atmospheric pressures inthe second step `may be bene` Aiicial.

Super-atmospheric pressures in `the .rst step may be employed to obtainhigher'temperatures. While some fractionation effected by the useof reux in the rst stage `is desirable, it is possi-ble and considered withinthe limits .of this invention, to carry out this operation, without reflux, e. g. by the use of a simple dashing `operation in a heated vessel, coil or 4othersuitable equipment. Suitable temperatures in this type ci operation are about the sameas when em ploying reiiux in a conventionaldistillation -co1- umn using reflux in the first step.

Exam-ple '1 This example will be described with reference to Figure l. A mixture `of octyl alcohols, prepared `by catalytic reaction `of carbon monoxide and hydrogen with C7 olelns with a composition such as that shown above, is fed by line I into an intermediate point of an alcohol stripper .frac- `which iis loperated -at atmospheric pressure. The-column temperature must be controlled vand heat .is 'added inanyl suitable manner, `for instance-by the fired-coil 3. A 'vapor temperature of the orderof 185 C. is maintained at the top oi the column. At a reflux ratio `of approximately 2 to l, an overhead product consisting of alcohol and certain other lower vboiling products including some aldehydic materials is removed by line 5. vIn the lower lportion Tof the column much `higher temperatures of the range of 2l5-320o C. are -maintained in order `to' decompose thermally the acetals, lhemi-acetals and certain other impurities whiohlare heat sensitive'and someof which lbreak Aup to yield addih tionalA octyl alcohol. A-bottoms product containing some alcohol, esters, oleiins, ethers and other more thermal stable `materials is removed `from stripper tower 4-2 `by lined. The'overhead product taken out byline 5 which is relatively high in the desired alcohol product,is-takenas quickly as possible by lines 5 and `ii to an intermediate point of a so-called heads column 1. `The product in line 5 Amay vbe subjected to a partial condensation before introducing it into column l' byline 6 but even this stepcan be avoided if Vthe transfer is immediate, as is most desirable to obtain the best purification. A part oi 'the alcohol product removed from column 2 lby overhead line 5 may be returned as reiuxtothecolumn 2 through inlet line I4. If some ylittletime will lapse before the second column step is to `be carried 'out,then a condensation will be desirable as the'lower temperatures thus obtained'will'tend to avoid recombination of the reactive aldehydic `materials present in the overhead from tower 2.

The ratio ofthe amounts of material `taken `as overhead 'from tower 2 to that taken 'out as lbottoms from tower 2 may be Variedsomewhat widely and will depend ngreat degree 'on the purity `of product desired, the further steps contemplated, and on the composition of the initial feed stock. It has been found that from 70% to 80% of the total feed can be taken overhead and, co1'- Vrespondingly, from to 30% removed as bottoms. VIt has further been found that the higher the percentage of material removed overhead, the more impure the final alcohol product obtained. This relationship seems to be true within limits.

The overhead material from tower 2 enters the heads column l at a point intermediate and preferably somewhat above the central portion. This column likewise is suitably heated as-by a heating coil 9. The overhead temperature is preferably kept low, of the order of 90-150 C. An overhead stream of volatiles containing some alcohol is removed by line 8 and condensed. A part or all of this overhead material can be returned as reflux to column 1 by lines l5 and l. In the preferred mode of operation, this should contain all materials boiling below 180 C. From the lower portion of the tower by line l0 there is removed the major portion of the desired alcohol with a small amount of bottoms product. The temperature in the lower portion of this column 1 should not exceed about 210 C. This cut from line l0 is taken directly to an auxiliary still Il from which o'ctyl alcohol of at least 98% purity is removed overhead by line i2 and condensed. A bottoms product from still Il is recycled by lines I3 and I back to stripper tower 2 to undergo a second thermal decomposition.

Example 2 This example can best be understood by read# ing it with reference to Figure 2. A feed mixture such as is used in Example 1 whosetypical composition is shown above, is fed by line 2l to an alcohol stripper column 22 at atmospheric pressure. The overheads product is taken by lines 25 and 2B directly to the heads column 21. The temperatures in tower 22 are controlled by heating coil 23 in the same desired ranges as for the tower 2 in Example 1. A bottoms product is removed through line 24. The overhead alcohol rich fraction from line 26 is fed to heads column 21 at an upper intermediate point. A part of this overhead fraction may be returned to column 22 by line 32 as-reilux. This column 21 is heated by a heating coil 29. From this column 21 the material boiling below 180 C. is removed overhead at a relatively high reflux ratio and at least a part of which may be returned to the column 21 as reflux by lines 33 and 34, while from a lower but intermediate portion of the column 21 there is removed by line 30 a desired octyl alcohol product having a boiling range of 180-195 C. The temperature in this portion of the column 21 should be controlled rather carefully to near the boiling range of the alcohol product. From the bottom of column 21 there is removed by line 3l a small amount of bottoms which is recycled by line 2| back to the alcohol stripper column 22. The temperature throughout column 21 should be kept as low as possible and even in the bottoms should not exceed about 220 C. The relative proportions of materials removed as the cuts from column 21 will vary somewhat depending on conditions of column 22Y operation, feed stock composition, and purity Yof product desired.

In a typical case where aboutf80% of the material put into column 22 was fed to column 21, 15% of volatiles was removed overhead, 60% was removed as desired octyl alcohol product, and

Vabout was taken out by line 3| as bottoms vfor recycle to column 22. Operating in this fashion,y an alcohol purity of not less than 98% was obtained. Where less material is taken from column 22 as overhead and fed to column 21, and more overhead is taken from column 21 as volatiles, an alcohol fraction of at least 99% is obtained.

What is claimed is:

l. An improved continuous distillation process for the purification of a mixture of crude alcohols containing high boiling unstable impurities and obtained by the reaction of olens with carbon monoxide and hydrogen and subsequent hydrogenation of the aldehydes resulting therefrom. which comprises introducing said mixture Yof crude alcohols into a primary stripping column, maintaining the bottoms temperature in said stripping column substantially above the normal boiling point of the alcohol, whereby substantial amounts of the high boiling unstable impurities are decomposed to volatile products, maintaining continuous reflux within the stripping column, removing an alcohol rich overhead vapor stream from said stripping column, passing said vapor stream immediately into a secondary column in which the temperatures are maintained substantially lower than those in the primary stripping column, removing as an overhead vapor stream substantially all volatiles boiling below the alcohol, removing an alcohol concentrate as a vapor stream from an intermediate portion of said secondary column, and recycling the bottoms product from the secondary column to the lower portion of the primary stripping column.

2. A continuous distillation process for the purification of a crude Cs alcohol containing high boiling heat unstable'impurities and obtained by the reaction of a mixture of C7 olefms with carbon monoxide and hydrogen and subsequent hydrogenation of the aldehydes resulting therefrom, which comprises introducing said crude Ca alcohol intov the intermediate portion of a primary fractionating column, maintaining temperatures of 285-320 C. in the bottom portion of said column whereby substantial amounts of the high boiling unstable impurities are decomposed to volatile products, maintaining continuous reflux within said primary fractionating column, remov- Y ing overhead an alcohol rich vapor stream, passing at least a portion of said alcohol rich vapor stream Vimmediately to a secondary column,l in which the temperatures are maintained substantially lower than those of the primary fractionating column, removing substantially all volatiles boiling appreciably below the `alcohol as an overhead vapor stream, removing a Ca alcohol concentrate as a vapor stream from an intermediate portion Vof said secondary column, and recycling the bottoms product of said secondary column to the lower portion of the primary fractionating column.

Y 3.l An improved continuous distillation process for the purification of a crude alcohol containing high-boiling impurities and obtained by the reaction of olens with carbon monoxide and hydrogen and subsequent hydrogenation of the aldehydes resulting therefrom, which comprises Yfeeding the said crude alcohol into an initial fractionation zone, maintaining the bottoms temperature in said initial fractionation zone substantially above the normal boiling point of the alcohol, maintaining continuous reflux within the initial fractionation zone, removing an alcohol-rich vapor stream essentially free of higherboiling unstable impurities from said initial purity fractionation zone, passing said alcohol-rich vapor stream immediately into a second fractionation zone, removing as an overhead vapor stream substantially all volatiles boiling below the alcohol from an upper portion of said second fractionation zone, and removing an alcohol-enriched vapor stream from a lower portion of said second fractionation zone.

4. An improved continuous distillation process for the purication of a mixture of crude alcohols containing high-boiling, unstable impurities and obtained by the reaction of olens with carbon monoxide and hydrogen and subsequent hydrogenation of the aldehydes resulting therefrom, which comprises introducing said mixture of crude alcohols into a primary fractionating column, maintaining the bottoms temperature in said primary fractionating column substantially above the normal boiling point of the alcohol, maintaining continuous reux Within said primary fractionating" column, removing an alcohol-rich overhead vapor stream from said primary fractionating column, passing said alcoholrich vapor stream immediately into `a secondary fractionating column in which the temperatures are maintained substantially lower than those in said primary fractionating column, removing substantially all volatiles boiling appreciably :beloW the alcohol from said secondary fractionating column as an overhead Vapor stream, passing the total bottoms of said secondary fractionating column including the alcohol to a third distillation zone, removing a purled alcohol vapor stream as an overhead product from said third distillation zone, and recycling the bottoms from said third distillation zone to an intermediate point of the primary fractionating column.

5. A continuous distillation process for the purication of a crude Ca alcohol containing high-boiling heat unstable impurities and obtained by the reaction of a mixture of Ci olefins with carbon monoxide and hydrogen and subsequent hydrogenation of the mixture of aldehydes resulting therefrom, which comprises introducing said ,crude Ca alcohol into the intermediate portion of a primary fractionating column, maintaining temperatures of 285--320o C. in the bottom portion of said primary fractionating column whereby substantial amounts of the high-boiling unstable impurities are decomposed to volatile products, maintaining continuous reflux within said primary fractionating column, removing overhead a Cs alcohol-rich vapor stream from said primary fractionating column, passing at least a portion of said Cs alcohol-rich vapor i0 stream immediately into a secondary column in which the temperatures are maintained substantially lower than those of the primary fractionating column, removing substantially all volatiles boiling appreciably below the Cs alcohol as an overhead vapor stream from said secondary column, passing the total bottoms of said secondary column including the alcohol into a third distillation zone, removing from said third distillation zone a puried C8 alcohol fraction as an overhead vapor stream, and recycling the bottoms product from thethird distillation zone to an intermediate point of said primary fractionating column. 6. An improved continuous distillation process for the purication of a mixture of crude alcohols containing high-boiling unstable impurities and obtained by the reaction of olens with carbon monoxide and hydrogen and subsequent hydrogenation of the aldehydes resulting therefrom which comprises introducing said mixture' of crude alcohols into a primary fractionating column, maintaining the bottoms temperature in said primary fractionating column substantially above the normal boiling point of the alcohol, maintaining continuous reux within said primary fractionating column, removing an alcohol-rich overhead vapor stream from said primary fractionating column, passing at least a portion of said vapor stream immediately into a second fractionating column in which the temperatures are maintained substantially lower than those in the primary fractionating column, removing as an overhead vapor stream from said secondary fractionating column substantially all volatiles boiling below the alcoholl removing an alcohol concentrate as -a distillate from highboiling bottoms of said secondary fractionating column, 4and recycling the high-boiling ibottoms product of the secondary fractionating column to a lower portion of the primary fractionating column.

CHARLES E. MORRELL. FRANK A. BIRIBAUER. CARL S. CARLSON.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,702,495 Clapp Feb. 19, 1929 2,186,617 Othmer Jan. 9, 1940 2,337,489 Patterson Dec. 21, 1943 2,417,886 Redcay Mar. 25, 1947 

3. AN IMPROVED CONTINUOUS DISTILLATION PROCESS FOR THE PURIFICATION OF A CRUDE ALCOHOL CONTAINING HIGH-BOILING IMPURITIES AND OBTAINED BY THE REACTION OF OLEFINS WITH CARBON MONOXIDE AND HYDROGEN AND SUBSEQUENT HYDROGENATION OF THE ALDEHYDES RESULTING THEREFROM, WHICH COMPRISES FEEDING THE SAID CRUDE ALCOHOL INTO AN INITIAL FRACTIONATION ZONE, MAINTAINING THE BOTTOMS TEMPERATURE IN SAID INITIAL FRACTIONATION ZONE SUBSTANTIALLY ABOVE THE NORMAL BOILING POINT OF THE ALCOHOL, MAINTAINING CONTINUOUS REFLUX WITHIN THE INITIAL FRACTIONATION ZONE, REMOVING AN ALCOHOL-RICH VAPOR STREAM ESSENTIALLY FREE OF HIGHERBOILING UNSTABLE IMPURITIES FROM SAID INITIAL FRACTIONATION ZONE, PASSING SAID ALCOHOL-RICH VAPOR STREAM IMMEDIATELY INTO A SECOND FRACTIONATION ZONE, REMOVING AS AN OVERHEAD VAPOR STREAM SUBSTANTIALLY ALL VOLATILES BOILING BELOW THE ALCOHOL FROM AN UPPER PORTION OF SAID SECOND FRAC- 